Contact probe, probe socket, electrical characteristic measuring device, and method for pushing the contact probe against object to be measured

ABSTRACT

A contact probe includes a probe tip and a damper. The probe tip includes a first barrel, a probe pin, and a first spring. The first barrel has a cavity with a bottom, an opening being disposed in a first end of the first barrel and the bottom being disposed at a second end of the first barrel. The probe pin is mounted in the first barrel so as to be movable forward and backward. The first spring is mounted in the cavity for elastically biasing the probe pin towards the opening. The damper is mounted to the second end of the first barrel, and elastically supports the first barrel.

This application is a divisional application of U.S. application Ser.No.: 10/859,282, filed on Jun. 2, 2004 now U.S. Pat. No. 7,116,123, andclaims the benefit of priority to Japanese Patent Application No.2003-163637, filed on Jun. 9, 2003, both of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to a contact probe, a probesocket, an electrical characteristic measuring device, and a method forpushing the contact probe against an object to be measured. Moreparticularly, an aspect of the present invention relates to a technologywhich makes it possible to mitigate electrostatic discharge damage ormechanical damage to an electronic device when measuring electricalcharacteristics of the electronic device.

2. Description of the Related Art

As shown in FIG. 14, a related electrical characteristic measuringdevice, such as a digital multimeter, comprises a body 61 incorporatingan electrical measuring unit, a measurement cable 62 drawn out from thebody 61, and a probe socket 63 connected to the measurement cable 62. Inthe example shown in FIG. 14, the probe socket 63 has two contact probes64 and 64. By pushing the contact probes 64 and 64 against, for example,terminals T₁ and T₂ of a thin-film magnetic head H (object to bemeasured), an electrical characteristic between the terminals T₁ and T₂can be measured.

In the related electrical characteristic measuring device shown in FIG.14, the measurement cable 62 may accumulate electrical charge because ithas an insulating film, and the contact probes 64 are in an easilychargeable state because they are in electrically floated states from apower source ground of the body 61. When the measurement cable 62 or thecontact probes 64 are charged, and the contact probes 64 and 64 contactthe terminals T₁ and T₂ of the thin-film magnetic head H, an electricalcharge Q moves momentarily. Even if the electrical charge Q that movesmomentarily is a small amount, a current value, which is a timedifferential of the electrical charge Q, is increased. The flow of alarge amount of current causes electrostatic discharge damage to thethin-film magnetic head H.

Contact probes having barrel structures are disclosed as means forpreventing electrostatic discharge damage in, for example, JapaneseUnexamined patent Application publication No. 2001-201515. Probes havingthe same structures as the contact probes disclosed in JapaneseUnexamined patent Application publication No. 2001-201515 is shown inFIG. 15. As shown in FIG. 15, contact probes 200 and 200 have respectiveprobe pins 201 and 201 and respective springs 202 and 202 disposed inrespective barrels 203 and 203. The probe pins 201 and 201 are biasedtowards respective ends 203 a and 203 a of the barrels by the respectivesprings 202 and 202. Ends of the probe pins 201 and 201 protrude fromthe respective barrels 203 and 203. The probe pins 201 and 201 areformed of high-resistance materials, and the barrels 203 and 203 areformed of low-resistance materials.

When the above-described contact probes are pushed against therespective terminals T₁ and T₂ of the thin-film magnetic head H, first,ends of the probe pins 201 and 201 come into contact with the respectiveterminals T₁ and T₂ of the thin-film magnetic head. Then, the probe pins201 and 201 push and compress the springs 202 and 202, and are pushedinto the respective barrels 203 and 203. At the same time that the probepins 201 and 201 are pushed into the respective barrels 203 and 203, theends 203 a and 203 a of the respective barrels come into contact withthe respective terminals T₁ and T₂. As a result of the barrels 203 and203 coming into contact with the respective terminals T₁ and T₂, anelectrical circuit is formed between the thin-film magnetic head H andthe electrical characteristic measuring device, and an electricalcharacteristic between the terminals T₁ and T₂ of the thin-film magnetichead H is measured.

When the ends of the respective probe pins 201 and 201 contact therespective terminals T₁ and T₂ of the thin-film magnetic head,electrical charges flow between the thin-film magnetic head H and theprobe pins 201 and 201. Since the probe pins 201 and 201 are formed ofhigh-resistance materials, the electrical current value at this time islow. Accordingly, since the electrical charges flow with a small currentvalue, and are removed before the barrels 203 and 203 come into contactwith their respective terminals T₁ and T₂, it is possible to preventelectrostatic discharge damage.

However, since the contact probes disclosed in Japanese Unexaminedpatent Application publication No. 2001-201515 are directly mounted tothe probe socket, they are formed so that force applied to the probesocket is directly applied to the contact probes. Therefore, when theprobe socket is strongly pushed against the terminals of the thin-filmmagnetic head, the ends of the barrels strongly contact the terminalsurfaces, thereby producing contact pressure which may damage theterminal surfaces.

In addition, as shown in FIG. 15, the positions of terminal surfaces T₁₁and T₂₂ of the thin-film magnetic head may not be aligned because ofstacking of dimensional tolerance at the time of manufacture. When onetries to measure electrical characteristics by pushing the probe socket63 against the non-aligned terminals T₁ and T₂, and the barrel end 203 aof one of the contact probes 200 contacts the terminal surface T₁₁, onlythe probe pin 201 of the other contact probe 200 may be in contact withthe terminal surface T₂₂. In this case, the probe pin 201 having highresistance is interposed in a measurement circuit system, therebypreventing precise measurements of the electrical characteristics.

SUMMARY OF THE INVENTION

An aspect of the present invention to provides a contact probe whichmakes it possible to measure electrical characteristics while preventingelectrostatic discharge damage to an object to be measured, a probesocket, an electrical characteristic measuring device, and a method forpushing the contact probe against the object to be measured.

According to an aspect of the present invention, a contact probe isprovided comprising a probe tip and a damper. The probe tip comprises afirst barrel, a probe pin, and a first spring. The first barrel has acavity with a bottom, an opening being disposed in a first end of thefirst barrel and the bottom being disposed at a second end of the firstbarrel. The probe pin is movable forward and backward in the cavity. Thefirst spring is mounted in the cavity such that it elastically biasesthe probe pin towards the opening. The damper is mounted to the secondend of the first barrel, and elastically supports the first barrel.Contact pressure produced when the first end of the first barrelcontacts an object to be measured is reduced by the damper.

The contact probe may be such that the damper comprises a second barrel,a plunger, and a second spring. The second barrel has a cavity with abottom, an opening being disposed in a first end of the second barreland the bottom being disposed at a second end of the second barrel. Theplunger is mounted in the second barrel so as to be movable forward andbackward, and is connected to the second end of the first barrel. Thesecond spring is mounted in the second barrel for elastically biasingthe plunger towards the opening of the second barrel. It may bedesirable that the forward and backward movement directions of theplunger and those of the probe pin be the same.

The first barrel may be elastically supported by the second springthrough the plunger, so that contact pressure of the first barrel can bereduced by the second spring. In addition, making the forward andbackward movement directions of the plunger and those of the probe pinthe same may make it possible to reduce the contact pressure of thefirst barrel.

The contact probe may be such that the damper comprises a second barrel,a plunger, and a second spring. The second barrel has a cavity with abottom, an opening being disposed in a first end of the second barreland the bottom being disposed at a second end of the second barrel. Theplunger is mounted in the second barrel so as to be movable forward andbackward. The second spring is mounted in the second barrel forelastically biasing the plunger towards the opening of the secondbarrel. The second end of the second barrel is connected to the secondend of the first barrel.

The first barrel may be elastically supported by the second springthrough the second barrel, so that contact pressure of the first barrelcan be reduced by the second spring. In a further aspect, integrallyforming the first and second barrels makes it possible to reduce thenumber of components of the contact probe.

In a contact probe according to an embodiment of the present invention,the spring constant of the second spring may be greater than the springconstant of the first spring. When the contact probe is pushed againstan object to be measured, the first spring is more easily compressedthan the second spring is compressed. When the first spring iscompressed, the first end of the first barrel comes into contact withthe object subsequent to the contacting of the probe pin. Then, thesecond spring is compressed, and the damper operates. Therefore, may bepossible to reliably bring the first barrel into contact with theobject, so that electrical characteristics can be measured.

In a contact probe according to an embodiment of the present invention,the sheet resistivity of the probe pin may be greater than the sheetresistivity of the first barrel. Since the sheet resistivity of theprobe pin is greater than that of the barrel, the electrical charges atan object to be measured and the contact probe itself may move slowlythrough the probe pin, so that the current value resulting from theelectrical charges can be kept low. Therefore, may be possible tomitigate electrostatic discharge damage to the object caused by contactof the contact probe.

In a contact probe according to an embodiment of the present invention,an end of the probe pin may be spherical. By virtue of the structure, anobject to be measured will not be scratched by contact of the probe pin.

According to another aspect of the present invention, there is provideda probe socket comprising a plurality of any one of the above-describedcontact probes. In the probe socket, the forward movement directions ofthe contact pins of the contact probes may be the same and the backwardmovement directions of the contact pins of the contact probes may be thesame, and the first ends of the first barrels may be aligned. Since theends of the first barrels contact an object to be measured at theapproximately same time, electrical characteristics can be measuredeffectively.

In a circumstance where the measurement surfaces of the object to bemeasured are not aligned, and only the first barrels of some of thecontact probes are in contact with respective measurement surfaces ofthe object (so that the first barrels of the other contact probes arenot in contact with respective measurement surfaces of the object), thedampers of the contact probes whose first barrels are in contact mayoperate to reduce the overall length of the contact probes themselves bythe action of further pushing the probe socket against the object.Accordingly, the first springs of the contact probes whose first barrelsare not in contact are compressed, so that the first barrels can bebrought into contact with the respective measurement surfaces of theobject. Therefore, it is possible to bring the first barrels of allcontact probes into contact with the object, so that electricalcharacteristics can be measured precisely.

According to a yet another aspect of the present invention, there isprovided an electrical characteristic measuring device comprising anyone of the above-described contact probes, or the above-described probesocket.

According to a still another aspect of the present invention, there isprovided a method for pushing a contact probe against a terminal of anelectronic-device. The method comprises the steps of bringing an end ofa probe pin into contact with the terminal, bringing a first end of afirst barrel into contact with the terminal while compressing a firstspring, and operating a damper. The contact probe comprises a probe tipand the damper. The probe tip comprises the first barrel, the probe pin,and the first spring. The first barrel has a cavity with a bottom, anopening being disposed in the first end of the first barrel and thebottom being disposed at a second end of the first barrel. The probe pinis movable forward and backward in the cavity. The first spring ismounted in the cavity for elastically biasing the probe pin towards theopening. The damper is mounted to the second end of the first barrel,and elastically supports the first barrel.

According to a method of the present invention, the damper may comprisea second barrel, a plunger, and a second spring. The second barrel has acavity with a bottom, an opening may be disposed in a first end of thesecond barrel and the bottom is disposed at a second end of the secondbarrel, the plunger may be mounted in the second barrel so as to bemovable forward and backward, and the second spring is mounted in thesecond barrel for elastically biasing the plunger towards the opening ofthe second barrel. In addition, the step of operating the damper maycomprise compressing the second spring and biasing the plunger towardsthe second end of the second barrel.

According to the above-described method, when the contact probe ispushed against an object to be measured, the first spring is more easilycompressed than the second spring is compressed. Then, the first end ofthe first barrel comes into contact with the object subsequent to thecontacting of the probe pin. Then, the second spring is compressed, andthe damper operates. Therefore, it is possible to reliably bring thefirst barrel into contact with the object, so that electricalcharacteristics can be measured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the structure of an electricalcharacteristic measuring device of a first embodiment;

FIG. 2 is a sectional schematic view of the structure of a contact probeof the electrical characteristic measuring device of the firstembodiment;

FIG. 3 is a sectional schematic view of the main portion of the contactprobe shown in FIG. 2;

FIG. 4 is a schematic view illustrating an operation of a probe socketin the first embodiment;

FIG. 5 is a schematic view illustrating another operation of the probesocket in the first embodiment;

FIG. 6 is a schematic view illustrating still another operation of theprobe socket in the first embodiment;

FIG. 7 is a schematic view illustrating still another operation of theprobe socket in the first embodiment;

FIG. 8 is a schematic view of the structure of an electricalcharacteristic measuring device of a second embodiment;

FIG. 9 is a sectional schematic view of the structure of a contact probeof the electrical characteristic measuring device of the secondembodiment;

FIG. 10 is a schematic view illustrating an operation of a probe socketin the second embodiment;

FIG. 11 is a schematic view illustrating another operation of the probesocket in the second embodiment;

FIG. 12 is a schematic view illustrating still another operation of theprobe socket in the second embodiment;

FIG. 13 is a schematic view illustrating still another operation of theprobe socket in the second embodiment;

FIG. 14 is a schematic view of the structure of a related electricalcharacteristic measuring device;

FIG. 15 is a schematic view of the structure of a related electricalcharacteristic measuring device; and

FIG. 16 is a schematic view illustrating the operation of the relatedelectrical characteristic measuring device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Several embodiments of the present invention will be described withreference to the relevant drawings. FIG. 1 shows the structure of anelectrical characteristic measuring device of a first embodiment. FIG. 2shows the structure of a contact probe of the electrical characteristicmeasuring device shown in FIG. 1. FIG. 3 is a sectional view of the mainportion of the contact probe.

As shown in FIG. 1, an electrical characteristic measuring device 1 of afirst embodiment comprises a body 2 incorporating an electricalmeasuring unit, a measurement cable 3 drawn out from the body 2, and aprobe socket 4 connected to the measurement cable 3. In the exampleshown in FIG. 1, the probe socket 4 has two contact probes 5 and 6. Bypushing the contact probes 5 and 6 against, for example, terminals of athin-film magnetic head (as an example of the object whosecharacteristics are to be measured), electrical characteristics betweenthe terminals can be measured.

The contact probes 5 and 6 have equivalent structures, so that thecontact probe 5 is only shown in FIG. 2. As shown in FIGS. 1 and 2, thecontact probes 5 and 6 comprise probe tips 11 a and 11 b and dampers 12a and 12 b, respectively. The probe tips 11 a and 11 b comprise,respectively, first barrels 21 a and 21 b, probe pins 22 a and 22 bmovable forward and backward in the respective first barrels 21 a and 21b, and first springs 23 a and 23 b for elastically biasing therespective probe pins 22 a and 22 b. The dampers 12 a and 12 b comprise,respectively, second barrels 31 a and 31 b, plungers 32 a and 32 bmovable forward and backward in the respective second barrels 31 a and31 b, and second springs 33 a and 33 b for elastically biasing therespective plungers 32 a and 32 b.

As shown in FIG. 1, the probe socket 4 may comprise the two contactprobes 5 and 6 and a body 4 a for holding the contact probes 5 and 6.The body 4 a has two socket portions 4 b and 4 b in which the secondbarrels 31 a and 31 b of the respective contact probes 5 and 6 areinserted. Probe terminals 4 c and 4 c are connected to the respectivesocket portions 4 b and 4 b, and the contact probes 5 and 6 areconnected to the respective measurement cables 3 and 3 through therespective probe terminals 4 c and 4 c.

The contact probes 5 and 6 are aligned so that the forward and backwardmovement directions of the probe pin 22 a and those of the probe pin 22b are the same with respect to the body 4 a, and so that first ends 21a, and 21 b, of the respective first barrels 21 a and 21 b are alignedwith respect to the body 4 a.

As shown in FIG. 2, the probe tip 11 a comprises the first barrel 21 a,the probe pin 22 a, and the first spring 23 a. The first barrel 21 a hasa cavity 21 a ₂ having a bottom. The cavity 21 a ₂ is formed so that thebottom is formed at a second end 21 a ₃ of the first barrel 21 a, andcommunicates with an opening 21 a ₄ in the first end 21 a ₁ of the firstbarrel. A stopper 21 a ₅ is disposed at the first end 21 a ₁ of thefirst barrel 21 a.

The probe pin 22 a is accommodated in the cavity 21 a ₂ of the firstbarrel 21 a, and is thinner than the opening 21 a ₄. An engager 22 a ₁is formed at a base end of the probe pin 22 a, and is stopped by thestopper 21 a ₅ as a result of engaging it with the stopper 21 a ₅. Anend 22 a ₂ of the probe pin 22 a is formed with a spherical shape.

The first spring 23 a is accommodated in the cavity 21 a ₂. One end ofthe first spring 23 a is communicates with the engager 22 a ₁ of theprobe pin, and the other end of the first spring 23 a communicates withan inner surface defining the cavity 21 a ₂. The inner surface may bethe bottom formed at the second end 21 a ₃ of the first barrel 21 a. Thefirst-spring 23 a elastically biases the probe pin 22 a towards theopening 21 a ₄. By stopping the engager 22 a ₁ of the probe pin 22 a bythe stopper 21 a ₅ as a result of engaging it with the stopper 21 a ₅,the probe pin 22 a is prevented from becoming dislodged from the firstbarrel 21 a. It is thus possible for the end 22 a ₂ of the probe pin toprotrude from the opening 21 a ₄, and for the probe pin 22 a to moveforward and backward in the first barrel 21 a.

The damper 12 a is mounted to the second end 21 a ₃ of the first barrel21 a and elastically supports the first barrel 21 a, and comprises thesecond barrel 31 a, the plunger 32 a, and the second spring 33 a. Thesecond barrel 31 a has a cavity 31 a ₂ having a bottom. The cavity 31 a₂ is formed so that the bottom is formed at a second end 31 a ₃ of thesecond barrel 31 a, and communicates with an opening 31 a ₄ in a firstend 31 a ₁ of the second barrel 31 a. A stopper 31 a ₅ is disposed atthe first end 31 a, of the second barrel 31 a. The side of the secondend 31 a ₃ of the second barrel 31 a corresponds to a socket receiver 31a ₆. The socket receiver 31 a ₆ is inserted in the socket portion 4 b ofthe probe socket 4.

The plunger 32 a is disposed in the cavity 31 a ₂ of the second barrel31 a, and is thinner than the opening 31 a ₄. An engager 32 a ₁ isformed at a base end of the plunger 32 a, and is stopped by the stopper31 a ₅ as a result of engaging the stopper 31 a ₅. A second spring 33 ais accommodated in the cavity 31 a ₂. One end of the second spring 33 acommunicates with the engager 32 a ₁ of the plunger, and the other endof the second spring 33 a communicates with an inner surface definingthe cavity 31 a ₂. The inner surface may be the bottom formed at thesecond end 31 a ₃ of the second barrel 31 a. The second spring 33 aelastically biases the plunger 32 a towards the opening 31 a ₄. Bystopping the engager 32 a ₁ of the plunger by the stopper 31 a ₅ as aresult of engaging it with the stopper 31 a ₅, the plunger 32 a isprevented from becoming dislodged from the second barrel 31 a. Theforward and backward movement directions of the plunger 32 a are thesame as those of the probe pin 22 a.

It is thus possible for an end of the plunger 32 a to protrude from theopening 31 a ₄, and for the plunger 32 a to move forward and backward inthe second barrel 31 a. In addition, the plunger 32 a is connected tothe second end 21 a ₃ of the first barrel 21 a, so that the first barrel21 a is elastically supported by the damper 12 a.

The probe pin 22 a is formed of a material having a sheet resistivitythat is greater than that of the material of the first barrel 21 a. Anexample of a specific material of the probe pin 22 a is a resincomposition having carbon fiber portions mixed in a thermoplastic resinmaterial. The carbon fiber portions have a thickness of 100 nm or less,and a ratio between the fiber length and the fiber thickness of 5 ormore. The amount of carbon fiber portions mixed in the thermoplasticresin material is desirably 0.1 to 8 parts by weight with respect to 100parts by weight of the thermoplastic resin material. At least one ofpolycarbonate, polybutylene terephthalate, polyethylene terephthalate,and polypropylene may be used for the thermoplastic resin material asmatrix resin.

The first barrel 21 a may be formed of, for example, a materialcomprising brass plated with gold, or other material having equivalentstructural and resistivity properties.

The sheet resistivity of the probe pin 22 a is may in the range of from10⁶ to 10¹² Ω/□ (ohms/square), and more desirably in the range of from10⁸ to 10¹⁰ Ω/□.

Sheet resistivity of the probe pin 22 a less than 10⁶ Ω/□ results inelectrical charges flowing with a high current value when the probe pin22 a contacts the object to be measured, which may cause electrostaticdischarge damage to the object. Sheet resistivity of the probe pin 22 agreater than 10¹² Ω/□ may delay the escape of the electrical charges.

As shown in FIG. 3, it may be desirable that a diameter R of the end 22a ₂ of the probe pin 22 a may be in the range of from 3.5 to 4 mm, andthat a maximum protruding height S of the probe pin 22 a from theopening 21 a ₄ may be in the range of from 0.15 to 0.25 mm. Since onlythe spherical portion of the end 22 a ₂ of the probe pin protrudes fromthe opening 21 a ₄, even if the probe pin 22 a is pushed into the firstbarrel 21 a, the probe pin 22 a may not contact the stopper 21 a ₅,thereby making it possible to prevent wearing of the stopper 21 a ₅.Other probe tip shapes may be used to achieve a desired contactpressure.

The spring constant of the second spring 33 a is greater than the springconstant of the first spring 23 a. The second spring 33 a may undergo astroke on the order of 0.3 mm when it is compressed by a load of 50 g to60 g. In contrast, the first spring 23 a may undergo a stroke on theorder of 0.3 mm when it is compressed by a load of 30 g. By setting thespring constants of the springs 23 a and 33 a as such, the first spring23 a is more easily compressed than the second spring 33 a iscompressed, so that the first end 21 a ₁ of the first barrel 21 a comesinto contact with the object to be measured subsequent to the contactingof the probe pin 22 a with the object, and, thereafter, the secondspring 33 a is further compressed in order to operate the damper 12 a.

Next, the operations of the contact probes 5 and 6, and the probe socket4 in the embodiment will be described. FIGS. 4, 5, 6, and 7 areschematic views for illustrating the operations of the probe socket 4 inthe embodiment.

First, as shown in FIG. 4, the probe socket 4 is brought closer to aterminal unit T of a thin-film magnetic head H (as an example of theobject whose characteristics are to be measured). The terminal unit T ofthe thin-film magnetic head may have two terminals T₁ and T₂. Terminalsurfaces T₁₁ and T₂₂ of the respective terminals T₁ and T₂ havedifferent heights, due to manufacturing tolerances or design. In theexample of FIG. 4, the terminal-surface T₁₁ is positioned closer to theprobe socket 4 than the terminal surface T₂₂.

As shown in FIG. 5, the probe socket 4 is brought even closer to theterminal unit T of the thin-film magnetic head H in order to bring theprobe pin 22 a of the contact probe 5 into contact with the terminalsurface T₁₁. Here, the probe pin 22 a and the terminal T₁ are broughtinto electrical conduction, so that electrical charges which may bepresent at the probe pin 22 a or the terminal T₁ flow through the probepin 22 a. Since the sheet resistivity of the probe pin 22 a isrelatively high, the electrical current value is kept small, therebymitigating electrostatic discharge damage to the thin-film magnetic headH.

As shown in FIG. 6, the probe socket 4 is brought even closer to theterminal unit T of the thin-film magnetic head H in order to bring theprobe pin 22 b of the contact probe 6 into contact with the terminalsurface T₂₂. At this time, in the contact probe 5, the probe pin 22 a ispushed into the first barrel 21 a as a result of compression of thefirst spring 23 a when the terminal T₁ and the probe socket 4 arebrought close to each other, so that the first end 21 a ₁ of the firstbarrel 21 a contacts the terminal T₁. Since the spring constant of thefirst spring 23 a is less than the spring constant of the second spring33 a, the first spring 23 a is more easily compressed than the secondspring 33 a is compressed. The motion continues until contact betweenprobe pin 22 b and terminal T₂ occurs.

Electrical conduction is achieved between the probe pin 22 b and theterminal T₂, so that electrical charges which may be present at theprobe pin 22 b or the terminal T₂ flow through the probe pin 22 b, whichmay mitigate electrostatic discharge damage to the thin-film magnetichead H.

Next, as shown in FIG. 7, when the probe socket 4 continues to bebrought still closer to the terminal unit T of the thin-film magnetichead H, the plunger 32 a is pushed into the second barrel 31 a as aresult of compression of the second spring 33 a of the contact probe 5,so that the contact probe 5 itself becomes shorter. At the same time,the first spring 23 b of the contact probe 6 is compressed, so that thefirst end 21 b ₁ of the first barrel 21 b comes into contact with theterminal surface T₂₂. Accordingly, the first barrels 21 a and 21 b ofthe respective contact probes 5 and 6 contact the terminals T₁ and T₂,respectively. Since the first barrels 21 a and 21 b are formed ofmaterials having relatively small sheet resistivity, voltage dropsbetween the terminal unit T and the contact probes 5 and 6 are reduced.

When the terminal surfaces T₁₁ and T₂₂ are not aligned, and the firstbarrel 21 a of the contact probe 5 is only in contact with the terminalsurface T₁₁ (so that the first barrel 21 b of the contact probe 6 is notin contact with the terminal surface T₂₂), by further pushing the probesocket 4 against the thin-film magnetic head H, the damper 12 a of thecontact probe 5 is operated to reduce the overall length of the contactprobe 5 itself. By this, the first spring 23 b of the contact probe 6 iscompressed, so that the first barrel 21 b can be brought into contactwith the terminal surface T₂₂. Therefore, it is possible to bring thefirst ends 21 a ₁ and 21 b ₁ of the first barrels into contact with theterminals T₁ and T₂, so that electrical characteristics can be measuredprecisely.

Since, as the probe socket 4 is moved closer to the terminal unit T ofthe thin-film magnetic head H, the plunger 32 a is pushed into thesecond barrel 31 a as a result of compression of the second spring 33 aof the contact probe 5, it is possible to reduce contact pressurebetween the first barrel 21 a of the contact probe 5 and the terminalsurface T₁₁, so that the terminal surface T₁₁ will not get scratched bythe first barrel 21 a.

Since, as described above, the first spring 23 a is more easilycompressed than the second spring 33 a is compressed when the contactprobe 5 is pushed against the terminal unit T, it is possible toreliably contact the first barrel 21 a with the terminal surface T₁₁, sothat electrical characteristics can be measured smoothly.

A second embodiment of the present invention will be described withreference to the relevant drawings. FIG. 8 shows the structure of anelectrical characteristic measuring device of the second embodiment.FIG. 9 shows the structure of a contact probe of the electricalcharacteristic measuring device shown in FIG. 8. Corresponding parts ofthe electrical characteristic measuring device, a contact socket, andthe contact probe to those of the electrical characteristic measuringdevice, the contact socket, and the contact probe having equivalentfunctions in the first embodiment are given the same reference numerals.Descriptions thereof will be either omitted or simplified.

As shown in FIG. 8, an electrical characteristic measuring device 101comprises a body 2, a measurement cable 3, and a probe socket 104. Inthe example shown in FIG. 8, the probe socket 104 has two contact probes105 and 106.

The contact probes 105 and 106 have equivalent structures, so that thecontact probe 105 is only shown in FIG. 9. As shown in FIGS. 8 and 9,the contact probes 105 and 106 comprise probe tips 111 a and 111 b anddampers 112 a and 112 b, respectively. The probe tips 111 a and 111 bcomprise, respectively, first barrels 121 a and 121 b, probe pins 22 aand 22 b movable forward and backward in the respective first barrels121 a and 121 b, and first springs 23 a and 23 b for elastically biasingthe respective probe pins 22 a and 22 b. The dampers 112 a and 112 bcomprise, respectively, second barrels 131 a and 131 b, plungers 132 aand 132 b movable forward and backward in the respective second-barrels131 a and 131 b, and second springs 33 a and 33 b for elasticallybiasing the respective plungers 132 a and 132 b.

As shown in FIG. 8, the probe socket 104 comprises the two contactprobes 105 and 106 and a body 4 a for holding the contact probes 105 and106. The body 4 a has two socket portions 4 b and 4 b in which theplungers 132 a and 132 b of the respective contact probes 105 and 106are inserted. Probe terminals 4 c and 4 c are connected to therespective socket portions 4 b and 4 b, and the contact probes 105 and106 are connected to the respective measurement cables 3 and 3 throughthe respective probe terminals 4 c and 4 c.

The contact probes 105 and 106 are aligned so that the forward andbackward movement directions of the probe pin 22 a and those of theprobe pin 22 b are the same with respect to the body 4 a, and so thatfirst ends 121 a ₁, and 121 b ₁ of the respective first barrels 121 aand 121 b are aligned with respect to the body 4 a.

As shown in FIG. 9, the probe tip 111 a comprises the first barrel 121a, the probe pin 22 a, and the first spring 23 a. The first barrel 121 ahas a cavity 121 a ₂ having a bottom. The cavity 121 a ₂ is formed sothat the bottom is comprised of a partition 140 formed at a second end121 a ₃ of the first barrel 121 a, and communicates with an opening 121a ₄, at the first end 121 a ₁ of the first barrel. A stopper 121 a ₅ isdisposed at the first end 121 a ₁ of the first barrel 121 a.

The probe pin 22 a is disposed in the cavity 121 a ₂ of the first barrel121 a. An engager 22 a ₁ is formed at a base end of the probe pin 22 a,and is stopped by the stopper 121 a ₅ as a result of engaging thestopper 121 a ₅.

The first spring 23 a is disposed in the cavity 121 a ₂. One end of thefirst spring 23 a communicates with the engager 22 a ₁ of the probe pin,and the other end of the first spring 23 a communicates with thepartition 140. The first spring 23 a elastically biases the probe pin 22a towards the opening 121 a ₄. By virtue of the structure, it ispossible for an end 22 a ₂ of the probe pin to protrude from the opening121 a ₄, and for the probe pin 22 a to move forward and backward in thefirst barrel 121 a.

The damper 112 a is mounted to the second end 121 a ₃ of the firstbarrel 121 a and elastically supports the first barrel 121 a, andcomprises the second barrel 131 a, the plunger 132 a, and the secondspring 33 a. The second barrel 131 a has a cavity 131 a ₂ having abottom. The cavity 131 a ₂ is formed so that the bottom is formed at asecond end 131 a ₃ of the second barrel 131 a, and communicates with anopening 131 a ₄ in a first end 131 a ₁ of the second barrel 131 a. Thecavities 121 a ₂ and 131 a ₂ of the respective first barrel 121 a andthe second barrel 131 a are divided by the partition 140.

A stopper 131 a ₅ is disposed at the first end 131 a ₁ of the secondbarrel 131 a. The side of an end 132 a ₃ of the plunger 132 acorresponds to a socket receiver 132 a ₄. The socket receiver 132 a ₄ isinserted in the socket portion 4 b of the probe socket 104.

The plunger 132 a is disposed in the cavity 131 a ₂ of the second barrel131 a. An engager 132 a ₁ is formed at a base end of the plunger 132 a,and is stopped by the stopper 131 a ₅ as a result of engaging thestopper 131 a ₅. The second spring 33 a is disposed in the cavity 131 a₂. One end of the second spring 33 a communicates with the engager 132 a₁ of the plunger, and the other end of the second spring 33 acommunicates with the partition 140. The second spring 33 a elasticallybiases the plunger 132 a towards the opening 131 a ₄. By stopping theengager 132 a ₁ of the plunger by the stopper 131 a ₅ as a result ofengaging it with the stopper 131 a ₅, the plunger 132 a is preventedfrom becoming dislodged from the second barrel 131 a.

By virtue of the structure, it is possible for the end 132 a ₃ of theplunger 132 a to protrude from the opening 131 a ₄, and for the plunger132 a to move forward and backward in the second barrel 131 a. Inaddition, the second barrel 131 a is connected to the first barrel 121a, so that the first barrel 121 a is elastically supported by the damper112 a.

As in the first embodiment, the probe pin 22 a may be formed of amaterial having a sheet resistivity that is greater than that of thematerial of the first barrel 121 a. The first barrel 121 a may be formedof the same material as the first barrel 21 a in the first embodiment.

A diameter R of the end 22 a ₂ of the probe pin 22 a, and a maximumprotruding height S of the probe pin 22 a may be set at values asindicated in the first embodiment. By virtue of the structure, itpossible to prevent wearing of the stopper 121 a ₅ caused by the probepin 22 a.

The spring constant of the second spring 33 a and the spring constant ofthe first spring 23 a may be set at values as indicated in the firstembodiment. The first spring 23 a is more easily compressed than thesecond spring 33 a is compressed, so that the first end 121 a ₁ of thefirst barrel 121 a comes into contact with an object to be measuredsubsequent to the contacting of the probe pin 22 a with the object, and,thereafter, the second spring 33 a is compressed in order to operate thedamper 112 a.

Next, the operations of the contact probes 105 and 106, and the probesocket 104 in the embodiment will be described. FIGS. 10, 11, 12, and 13are schematic views for illustrating the operations of the probe socket104 in the embodiment.

First, as shown in FIG. 10, the probe socket 104 is brought closer to aterminal unit T of a thin-film magnetic head H (as an example of anobject whose characteristics are to be measured). Next, as shown in FIG.11, the probe socket 104 is brought even closer to the terminal unit Tof the thin-film magnetic head H in order to bring the probe pin 22 a ofthe contact probe 105 into contact with a terminal surface T₁₁. Theprobe pin 22 a and the terminal T₁ are then brought into electricalcontact, so that electrical charges which may be present at the probepin 22 a or the terminal T₁ flow through the probe pin 22 a. Since thesheet resistivity of the probe pin 22 a is relatively high, theelectrical current value is kept small, thereby mitigating electrostaticdischarge damage to the thin-film magnetic head H.

Next, as shown in FIG. 12, the probe socket 104 is brought even closerto the terminal unit T of the thin-film magnetic head H in order tobring the probe pin 22 b of the contact probe 106 into contact with aterminal surface T₂₂. At this time, in the contact probe 105, the probepin 22 a is pushed into the first barrel 121 a as a result ofcompression of the first spring 23 a when the terminal unit T and theprobe socket 104 are brought close to each other, so that the first end121 a ₁ of the first barrel 21 a contacts the terminal T₁. Since thespring constant of the first spring 23 a is less than the springconstant of the second spring 33 a, the first spring 23 a is more easilycompressed than the second spring 33 a is compressed.

Electrical conduction is achieved between the probe pin 22 b and theterminal T₂, so that electrical charges which may be present at theprobe pin 22 b or the terminal T₂ flow through the probe pin 22 b,thereby mitigating electrostatic discharge damage to the thin-filmmagnetic head H.

Next, as shown in FIG. 13, when the probe socket 104 is brought evencloser to the terminal unit T of the thin-film magnetic head H, theplunger 132 a is pushed into the second barrel 131 a as a result ofcompression of the second spring 33 a of the contact probe 105, so thatthe contact probe 105 itself becomes shorter. At the same time, thefirst spring 23 b of the contact probe 106 is compressed, so that thefirst end 121 b ₁ of the first barrel 121 b comes into contact with theterminal surface T₂₂. Accordingly, the first barrels 121 a and 121 b ofthe respective contact probes 105 and 106 contact the terminals T₁ andT₂, respectively. Since the first barrels 121 a and 121 b are formed ofmaterials having relatively small sheet resistivity, voltage dropsbetween the terminal unit T and the contact probes 105 and 106 arereduced.

When the terminal surfaces T₁₁ and T₂₂ are not aligned, and the firstbarrel 121 a of the contact probe 105 is only in contact with theterminal surface T₁₁ (so that the first barrel 121 b of the contactprobe 106 is not in contact with the terminal surface T₂₂), by furtherpushing the probe socket 104 against the thin-film magnetic head H, thedamper 112 a of the contact probe 105 is operated to reduce the overalllength of the contact probe 105 itself. By this, the first spring 23 bof the contact probe 106 is compressed, so that the first barrel 121 bcan be brought into contact with the terminal surface T₂₂. Therefore, itis possible to bring the first ends 121 a ₁ and 121 b ₁ of the firstbarrels 121 a and 121 b into contact with the terminals T₁ and T₂, sothat electrical characteristics can be measured.

Since, as the probe socket 104 is moved closer to the terminal unit T ofthe thin-film magnetic head H, the plunger 132 a is pushed into thesecond barrel 131 a as a result of compression of the second spring 33 aof the contact probe 105, it is possible to reduce contact pressurebetween the first barrel 121 a of the contact probe 105 and the terminalsurface T₁₁, so that the terminal surface T₁₁ will may not be scratchedby the first barrel 121 a.

Since, as described above, the first spring 23 a is more easilycompressed than the second spring 33 a is compressed when the contactprobe 105 is pushed against the terminal unit T, it is possible toreliably contact the first barrel 121 a with the terminal surface T₁₁,so that electrical characteristics can be measured smoothly.

The scope of the present invention is not limited to the above-describedembodiments, so that various modifications may be made within the scopeof the present invention. For example, although, in each of theabove-described embodiments, a probe socket having two contact probes isexplained, a contact socket having three or more contact probes may alsobe used in the present invention.

Although the description of the contact probe has been described in thecontext where a fist probe contacts a first corresponding terminal priorto a second probe contacting a second corresponding terminal due to alinear offset in the distances to be traversed between the probes andthe terminals, such a situation may also result from an angular offsetof the probe socket from the surface to which the terminals are mounted,or a combination of the two situations.

As can be further understood from the foregoing description, in thecontact probe in the present invention, a damper elastically supportingthe first barrel is mounted to the second end of the first barrel of theprobe tip, so that contact pressure produced when the first end of thefirst barrel contacts an object to be measured is reduced by the damper,as a result of which the object may not be scratched.

1. A contact probe comprising: a probe tip comprising a first barrel, aprobe pin, and a first spring; and a damper, wherein the first barrelcomprises first and second ends; and the damper comprises a secondbarrel, a plunger, and a second spring, the second barrel has a cavitywith a second bottom, an opening is disposed in a first end of thesecond barrel and the second bottom is disposed at a second end of thesecond barrel, the plunger is mounted in the second barrel so as to bemovable forward and backward, the second spring is mounted in the secondbarrel for elastically biasing the plunger towards the opening of thesecond barrel, and the second end of the second barrel is connected tothe second end of the first barrel.
 2. The contact probe according toclaim 1, wherein the second end of the first barrel and the second endof the second barrel are conjoined.
 3. The contact probe according toclaim 1, wherein the second end of the first barrel and the second endof the second barrel are an integral portion.
 4. The contact probeaccording to claim 3, wherein the integral portion is disposed betweenthe first and second springs.
 5. The contact probe according to claim 1,wherein the spring constant of the second spring is greater than thespring constant of the first spring.
 6. The contact probe according toclaim 1, wherein the ratio of the spring constant of the second springto the spring constant of the first spring is approximately 2.